it has been a growing concern for telephone subscribers of multiple units on a single line that their rights to private communication are jeopardized by unsuspecting ears on other units. This fear is balanced against the practical efficiency of having multiple units coupled with or to the same extension line. Multiple units on the same line serve well to provide telephone convenience to a broader geographical area and to provide communication in a conference setting wherein multiple parties may be on line simultaneously. However, where the specific operating environment has particular requirements for privacy, it is often desirable that all but one phone be excluded from the line when private communication is conducted via that one phone.
A number of advances in the telephone art occurred in the recent past when a privacy exclusion circuit was adopted for telephone units coupled on the same extension line. This system has special application in key telephone systems wherein an extension phone may come on line by depressing a key on the extension set. These prior art systems unilaterally adopt a scheme wherein the first phone taken offhook to answer an incoming call or to initiate a call seizes the telephone line and prevents all other extension phones from coming on line. In this manner, confidentiality is assured and private communications are implemented for each user who manages to obtain an active line.
While such systems have, to a certain extent, achieved privacy in communications, room for significant and meaningful improvement exists.
The systems of the prior art are not flexible. First, a user does not exercise control over whether other units should remain connected to the phone line once a conversation starts. Second, the capability of connecting and disconnecting other telephones is limited to one reconnection. Third, all units are necessarily affected by such prior art systems; no means is provided for certain units to operate as master sets and/or slave sets. Fourth, prior art systems are not modular in their connection to the telephone line.
The problems suggested in the preceding are not intended to by exhausting, but rather among many which may tend to detract from the usefulness of prior systems supporting privacy on an extension line having multiple units coupled thereto. Other noteworthy problems may exist. However, those presented above should be sufficient to demonstrate that implementations of privacy communication on a telephone line supporting multiple units have not been altogether satisfactory.